1. Field of the Disclosure
The present invention relates to a touch panel control circuit and a semiconductor integrated circuit including the same, and particularly to, a touch panel control circuit which can be suitably used as a touch panel control circuit connected to a touch panel mounted in a display panel so as to overlap therewith.
2. Description of the Related Art
In a display panel that is used in a smart phone or a tablet terminal, a touch panel is mounted so as to overlap the display panel, and a user can operate an apparatus by touching (touching or tracing on) a display screen with a finger and the like. The touch panel control circuit is connected to the touch panel and detects coordinates on the display screen that is touched by the user. For example, in a mutual-capacitance type touch panel, a Y electrode as a drive electrode and an X electrode as a detection electrode are disposed perpendicular to each other with a dielectric interposed therebetween, and a capacitor (intersection capacitor) is configured in each intersection. If capacitance due to a finger or a hand is present in the vicinity of the intersection capacitor, mutual capacitance at the intersection is reduced from a capacitance value of the intersection capacitor by a division amount of electric charges that are charged by the capacitance by the finger or the hand. The touch panel control circuit detects at which intersection a variation of the mutual capacitance occurs and to what magnitude.
JP-A-2012-234474 and JP-A-2012-59265 disclose a technology for improving detection sensitivity or detection accuracy in a touch panel control circuit connected to the touch panel that is mounted in a display panel so as to overlap therewith.
In a touch panel control circuit that is disclosed in JP-A-2012-234474, a pulse-shaped AC drive voltage is repetitively applied to an intersection capacitor from a Y electrode, and electric charges corresponding to a capacitance value of the intersection capacitor at that time are transmitted and are accumulatively added by an integration circuit connected to the X electrode. In this manner, detection is performed. At this time, the amplitude of the drive AC voltage that is applied is increased to increase the signal level (amount of electric charges that are transmitted), and the timing between signals that drive the display panel is retarded in order to decrease a noise level that is affected by a display drive signal, thereby improving a signal/noise ratio (S/N ratio).
In a display device disclosed in JP-A-2012-59265, a display panel operating period and a touch sensing period are divided in a time division manner, thereby preventing a display drive signal having an effect on touch detection as a noise.